Dielectric ceramic composition for high frequencies

ABSTRACT

A dielectric ceramic composition for high frequencies comprises a main component of a TiO 2  -ZrO 2  -Sn 2  O system and contains, as additives, not more than 7 wt % of ZnO, not more than 10 wt % of NiO, and not more than 7 wt % of one metal oxide selected from the group consisting of Nb 2  O 5 , Ta 2  O 5 , WO 3  and Sb 2  O 5 . The main component consists essentially of 22 to 43 wt % of TiO 2 , 38 to 58 wt % of ZrO 2 , and 9 to 26 wt % of SnO 2 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dielectric ceramic composition for highfrequencies. More particularly, the present invention relates to animproved dielectric ceramic composition which possesses a highdielectric constant and a high Q value even in a high frequency regionof microwaves and millimetric waves.

2. Description of the Prior Art

In a high frequency region, various dielectric ceramics are widely usedfor dielectric resonators, dielectric substrates for microwaveintegrated circuits, and the like because of their useful electricalproperties. In recent years, there have been trends to use higherfrequencies in microwave systems, and there is an increasing demand fordielectric ceramics with better electrical properties.

To this end a ceramic composition of a system TiO₂ -ZrO₂ -SnO₂ -Zno-NiOhas been developed as a dielectric material for high frequencies and isdisclosed in Japanese publication No. 55-34526. However, a flow Q valueat high frequenceis of this material makes its general use impossible.For example, the Q values of this material are 25000 at 1 GHz, 12000 at4 GHz, and 7000 at 7 GHz. Thus, when this material is used fordielectric resonators in a high power circuit operated at a lowfrequency, e.g., at 800 MHz, it generates a large amount of heat, thusmaking its stable operation impossible. Also, the Q value of thismaterial is too low to use it as dielectric resonators operated at afrequency of 4 GHz or 10 GHz.

In order to solve this problem, it has been proposed to replace ZnO orNiO with Ta₂ O₅ in the system TiO₂ -ZrO₂ -SnO₂ -ZnO-NiO in Japanesepatent laid-open Nos. Nos. 58-51406 and 58-217465. The formercomposition consists essentially of a main component composed of 22 to43 weight percent (wt %) of TiO₂, 38 to 58 wt % of ZrO₂ and 9 to 26 wt %of SnO₂, and additives of not more than 7 wt % of ZnO and not more than5 wt % of Ta₂ O₅. The latter differs from the former in that theadditives consists of not more than 10 wt % of NiO and not more than 5wt % of Ta₂ O₅.

The replacement of ZnO or NiO in the TiO₂ -ZrO₂ SnO₂ -ZnO-NiO systemwith Ta increases the Q value in some degree, but the maximum Q value ofthese materials is 8000 at 7GHz. In addition, there is still room forimprovement in their sintering properties.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide adielectric ceramic composition for high frequencies which possesses ahigher Q value even in a microwave frequency region and has improvedsintering properties.

Another object of the present invention is to provide a dielectricceramic composition for high frequencies having a relatively highdielectric constant, a high Q value and improved sintering properties.

According to the present invention these and other objects are solved byincorporating additives composed of not more than 7 wt % of ZnO, notmore than 10 wt % of NiO and not more than 7 wt % of one metal oxideselected from the group consisting of Nb₂ O₅, Ta₂ O₅, WO₃ and Sb₂ O₅into a basic composition consisting essentially of 22 to 43 wt % ofTiO₂, 38 to 58 wt % of ZrO₂, and 9 to 26 wt % of SnO₂.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

According to a preferred embodiment of the present invention, there isprovided a dielectric ceramic composition consisting essentially of amain component of a TiO₂ -ZrO₂ -Sn₂ O system, and additives composed ofZnO, NiO and Nb₂ O₅, the main component being composed of 22 to 43 wt %of TiO₂, 38 to 58 wt % of ZrO₂, and 9 to 26 wt % of SnO₂, the content ofZnO being not more than 7 wt %, the content of NiO being not more than10 wt %, the content of Nb₂ O5 being not more than 5 wt %.

In another preferred embodiment, a dielectric ceramic compositionconsists essentially of a main component composed of 22 to 43 wt % ofTiO₂, 38 to 58 wt % of ZrO₂ and 9 to 26 wt % of SnO₂, and additivescomposed of ZnO, NiO and Ta₂ O₅, the content of ZnO being not more than7 wt %, the content of NiO being not more than 10 wt %, the content ofTa₂ O₅ being not more than 7 wt %.

In further embodiment of the present invention, a dielectric ceramiccomposition consists essentially of a main component composed of 22 to43 wt % of TiO₂, 38 to 58 wt % of ZrO₂ and 9 to 26 wt % of SnO₂, andadditives composed of ZnO, NiO and Sb₂ O₅, the content of ZnO being notmore than 7 wt %, the content of NiO being not more than 10 wt %, thecontent of Sb₂ O₅ being not more than 7 wt %.

In still another preferred embodiment, a dielectric ceramic compositionconsists essentially of a main component composed of 22 to 43 wt % ofTiO₂, 38 to 58 wt % of ZrO₂ and 9 to 26 wt % of SnO₂, and additivescomposed of ZnO, NiO and WO₃, the content of ZnO being not more than 7wt %, the content of NiO being not more than 10 wt %, the content of WO₃being not more than 7 wt %.

The reasons why the composition of the main component has been limitedto the above range are as follows: If the content of TiO₂ is less than22 wt %, the dielectric constant becomes lowered. If the content of TiO₂is more than 43 wt %, the temperature coefficient of dielectric constantbecomes too large on the positive side. If the content of ZrO₂ is lessthan 38 wt % or more than 58 wt %, the temperature coefficient ofdielectric constant becomes too large on the positive side. If thecontent of SnO₂ is less than 9 wt %, the temperature coefficient ofdielectric constant becomes too large on the positive side, and the Qvalue becomes lowered. If the content of SnO₂ is more than 26 wt %, thetemperature coefficient of dielectric constant becomes too large on thenegative side.

The contents of respective additives have been limited as being in theabove respective ranges for the following reasons.

In the composition containing ZnO, NiO and Nb₂ O₅ as the additives, ifthe content of ZnO exceeds 7 wt % with respect to the amount of the maincomponent, the dielectric constant and Q become lowered. If the contentof NiO is more than 10 wt %, or if the content of Nb₂ O₅ is more than 5wt % with respect to the amount of the main component, the Q becomes toolow to put the composition into practical use.

In the composition containing ZnO, NiO and Ta₂ O₅ as the additives, ifthe content of ZnO exceeds 7 wt % with respect to the amount of the maincomponent, the dielectric constant and Q become lowered. If the contentof NiO is more than 10 wt %, or if the content of Ta₂ O₅ is more than 7wt % with respect to the amount of the main component, the Q becomes toolow to put the composition into practical use.

In the composition containing ZnO, NiO and WO₃ as the additives, if thecontent of ZnO exceeds 7 wt % with respect to the amount of the maincomponent, the dielectric constant and Q become lowered. If the contentof NiO is more than 10 wt %, or if the content of WO₅ is more than 7 wt% with respect to the amount of the main component, the Q becomes toolow to put the composition into practical use.

In the composition containing ZnO, NiO and Sb₂ O₅ as the additives,their contents have been limited as being in the respective aboveranges, for the following reasons. If the content of ZnO exceeds 7 wt %with respect to the amount of the main component, the dielectricconstant and Q become lowered. If the content of NiO is more than 10 wt%, or if the content of Sb₂ O₅ is more than 7 wt % with respect to theamount of the main component, the Q becomes too low to put thecomposition into practical use.

The present invention makes it possible to produce dielectric ceramiccompositions having a high Q value even at high frequencies, stablesintering properties, and uniform and small crystal grain sizes. Forexample, the ceramics of the present invention possesses a high Q valueof 9000 at 7 GHz with a temperature coefficient of resonant frequency[TC(fo)] of about 0 ppm/°C. These advantages result from the addition ofadditives mentioned above which contribute to make the grain growthuniform and to inhibit formation of lattice irregularities in the graincrystals. The dielectric ceramic composition of the present inventionhas a relatively high dielectric constant of about 40 in addition to thehigh Q value and small temperature coefficient.

Thus, the dielectric ceramic composition of the present invention can beused widely in the field of mobile phones operated at a frequency of 800MHz and even in that of direct broadcasting by satellite operated at afrequency of 4 GHz or 10 GHz. For example, the dielectric ceramiccomposition of the present invention can be used for dielectricresonators inserted in high power channel filter circuits ofground-support equipment for mobile phones.

These and other features and advantages of the present invention will bemore apparent from the following description with reference to thepreferred embodiments thereof.

BRIEF EXPLANATION OF THE DRAWINGS

FIGS. 1 to 4 are graphs showing variations of the Q value with frequencyfor dielectric ceramic compositions of the present invention.

EXAMPLE 1

Using highly purified oxides TiO₂, ZrO₂, SnO₂, ZnO, NiO and Nb₂ O₅ asraw materials, there were prepared mixtures so that each of theirsintered bodies has a composition shown in Table 1. Each resultingmixture was wet milled in a mill for 16 hours, dehydrated, dried andthen pressed into discs having a diameter of 12 mm and a thickness of 6mm under a pressure of 2500 kg/cm². The discs were fired in naturalatmosphere at 1350° to 1450° C. for 4 hours to prepare ceramic discs.

Each resultant ceramic disc was subjected to measurements of electricalproperties. The measurements were made on the dielectric constant (ε),quality factor (Q) and temperature coefficient of resonant frequency[TC(fo)].

The dielectric constant (ε) and Q value were measured at 25° C. and at 7GHz by a well-known dielectric resonator method. The temperaturecoefficient of resonant frequency [TC(fo)] was determined by theequation:

    TC (fo)=1/2TC(ε)-α

where TC(ε) is a temperature change rate of dielectric constant measuredin a temperature range of +25° to +85° C., and α is a thermalcoefficient of linear expansion of the ceramics.

Results are shown in Table 1. In the table, asterisked specimens arethose having a composition beyond the scope of the present invention,while other specimens are those included in the scope of the presentinvention.

For the specimens Nos. 14 and 23, measurements of electrical propertieswere not carried out since it is impossible to sinter them.

                                      TABLE 1                                     __________________________________________________________________________    Specimen                                                                      No.  TiO.sub.2                                                                        ZrO.sub.2                                                                         SnO.sub.2                                                                        ZnO                                                                              NiO                                                                              Nb.sub.2 O.sub.5                                                                  ε                                                                        Q  TC(× 10.sup.-6 /°C.)              __________________________________________________________________________     1*  20 56  24 1.0                                                                              0.2                                                                              0.5 31.5                                                                             6600                                                                             -14                                             2   22 52  26 2.0                                                                              5.0                                                                              3.0 31.0                                                                             6900                                                                             -10                                             3   22 58  20 3.0                                                                              6.0                                                                              5.0 27.5                                                                             5300                                                                             +33                                             4*  22 58  20 8.0                                                                              5.0                                                                              6.0 26.5                                                                             2200                                                                             +41                                             5   28 48  24 1.0                                                                              0.5                                                                              0.5 31.2                                                                             7900                                                                             -14                                             6   28 56  16 5.0                                                                              3.0                                                                              1.0 30.2                                                                             5600                                                                             +17                                             7*  32 52  16 0.5                                                                              20.0                                                                             6.0 26.8                                                                             2200                                                                              -8                                             8   32 52  16 2.0                                                                              3.0                                                                              3.0 31.4                                                                             7700                                                                              -4                                             9   32 52  16 2.0                                                                              10.0                                                                             5.0 30.3                                                                             5000                                                                              +2                                             10* 32 52  16 10.0                                                                             3.0                                                                              2.0 26.0                                                                             3000                                                                              -1                                            11   33 58   9 2.0                                                                              4.0                                                                              3.0 35.8                                                                             4000                                                                             +26                                            12   36 38  26 3.0                                                                              1.0                                                                              1.0 36.2                                                                             7200                                                                              +6                                            13   38 48  14 1.0                                                                              0.5                                                                              2.0 37.0                                                                             8000                                                                              +2                                             14* 38 48  14 10.0                                                                             20.0                                                                             6.0 not sintered                                          15* 40 36  24 1.0                                                                              0.5                                                                              0.5 40.2                                                                             4600                                                                             +82                                            16   40 39  21 0.5                                                                              0.2                                                                              1.0 37.8                                                                             8800                                                                              -1                                            17   40 39  21 1.0                                                                              0.5                                                                              3.0 37.0                                                                             8600                                                                              -4                                             18* 40 39  21 2.0                                                                              20.0                                                                             4.0 22.4                                                                             1800                                                                              +3                                             19* 40 39  21 7.0                                                                              5.0                                                                              6.0 24.2                                                                             2300                                                                             -16                                            20   40 44  16 1.0                                                                              0.5                                                                              2.0 36.5                                                                             8400                                                                              +2                                            21   43 38  19 1.0                                                                              0.5                                                                              0.5 37.6                                                                             6700                                                                             +47                                            22   43 48   9 0.5                                                                              3.0                                                                              1.0 39.2                                                                             6000                                                                             +20                                             23* 43 48   9 0.5                                                                              20.0                                                                             6.0 not sintered                                         24   43 48   9 2.0                                                                              10.0                                                                             1.0 37.2                                                                             4800                                                                             +22                                             25* 43 48   9 10.0                                                                             10.0                                                                             6.0 34.0                                                                             1000                                                                             +19                                            __________________________________________________________________________

From the results shown in Table 1, the dielectric composition of thepresent invention have a high Q value even at high frequencies andstable sintering properties. For example, the specimen No. 16 has a Qvalue of 8800 at 7 GHz and a temperature coefficient of resonantfrequency [TC(fo)] of about 0 ppm/°C.

For comparison, there was prepared a comparative specimen having acomposition consisting of a main component composed of 38 wt % of TiO₂,48 wt % of ZrO₂ and 14 wt % of SnO₂, and additives of ZnO and NiO, thecontent of ZnO being 1.0 wt %, the content of NiO being 0.5 wt %.

For the specimen No. 16, and the above comparative specimen,measurements were made on the quality factor (Q) at frequencies rangingfrom 0.5 GHz to 7 GHz. Results are shown in FIG. 1 as a function offrequency.

From the results shown in FIG. 1, it will be seen that the dielectricceramic composition according to the present invention is improved inthe quality factor (Q). In particular, the quality factor (Q) increasesquite rapidly with lowering of frequency and takes values of 39,000 at 1GHz, 16,500 at 4 GHz, and 8800 at 7 GHz, which are respectivelyincreased by 56%, 38%, and 26 wt % of those of the comparative specimen.

For the specimen No. 16 measurements were made on crystal grain sizesand mechanical strength. It was found that this composition has a grainsize distribution ranging from 5 to 10 μm and a mechanical strength of1200 Kg/cm². Thus, it will be seen that the incorporation of Nb₂ O₅together with ZnO and NiO makes it possible to obtain dielectricceramics with a fine crystal grain size and a large strength. In otherwords, the addition of these additives also contribute to make the graingrowth uniform and to inhibit formation of lattice irregularities in thegrain crystals.

EXAMPLE 2

Using highly purified oxides TiO₂, ZrO₂, SnO₂, ZnO, NiO and Ta₂ O₅ asraw materials, mixtures of raw materials were so prepared that each oftheir sintered bodies has a composition shown in Table 2. Each resultingmixture was milled by the wet process in a mill for 16 hours,dehydrated, dried and then pressed into discs having a diameter of 12 mmand a thickness of 6 mm under a pressure of 2500 kg/cm². The discs werefired in natural atmosphere at 1350 to 1450° C. for 4 hours to prepareceramic discs.

Each resultant ceramic disc was subjected to measurements of electricalproperties. The measurements were made on the dielectric constant (ε),quality factor (Q) and temperature coefficient of resonant frequency[TC(fo)] in the same manner under the same conditions as in Example 1.Results are shown in Table 2.

In the table, asterisked specimens are those having a composition beyondthe scope of the present invention, while other specimens are thoseincluded in the scope of the present invention.

For the specimens Nos. 39 and 48, measurements of electrical propertieswere carried out since it is impossible to sinter them.

                                      TABLE 2                                     __________________________________________________________________________    Specimen                                                                      No.  TiO.sub.2                                                                        ZrO.sub.2                                                                         SnO.sub.2                                                                        ZnO                                                                              NiO                                                                              Ta.sub.2 O.sub.5                                                                  ε                                                                        Q  TC(× 10.sup.-6 /°C.)              __________________________________________________________________________     26* 20 56  24 1.0                                                                              0.2                                                                              0.5 33.0                                                                             6900                                                                             -12                                            27   22 52  26 2.0                                                                              5.0                                                                              5.0 31.4                                                                             7000                                                                             -11                                            28   22 58  20 3.0                                                                              6.0                                                                              7.0 28.6                                                                             5500                                                                             +31                                             29* 22 58  20 8.0                                                                              5.0                                                                              10.0                                                                              25.0                                                                             2400                                                                             +40                                            30   28 48  24 1.0                                                                              0.5                                                                              0.5 31.0                                                                             7800                                                                             -12                                            31   28 56  16 5.0                                                                              3.0                                                                              2.0 30.2                                                                             5800                                                                             +19                                             32* 32 52  16 0.5                                                                              20.0                                                                             1.0 28.7                                                                             2000                                                                              -6                                            33   32 52  16 2.0                                                                              3.0                                                                              3.0 30.8                                                                             7500                                                                              -2                                            34   32 52  16 2.0                                                                              10.0                                                                             5.0 30.0                                                                             5200                                                                              +1                                             35* 32 52  16 10.0                                                                             3.0                                                                              10.0                                                                              25.2                                                                             2500                                                                              -2                                            36   33 58   9 2.0                                                                              4.0                                                                              4.0 35.5                                                                             5000                                                                             +28                                            37   36 38  26 3.0                                                                              1.0                                                                              1.0 35.0                                                                             7600                                                                              +7                                            38   38 48  14 1.0                                                                              0.5                                                                              1.0 38.2                                                                             8200                                                                              +2                                             39* 38 48  14 10.0                                                                             20.0                                                                             6.0 not sintered                                          40* 40 36  24 1.0                                                                              0.5                                                                              0.5 40.5                                                                             5000                                                                             +80                                            41   40 39  21 0.5                                                                              0.2                                                                              1.0 38.0                                                                             9000                                                                               0                                            42   40 39  21 1.0                                                                              0.5                                                                              2.0 36.2                                                                             8800                                                                              -2                                             43* 40 39  21 2.0                                                                              20.0                                                                             7.0 24.6                                                                             2000                                                                              +8                                             44* 40 39  21 7.0                                                                              5.0                                                                              10.0                                                                              25.5                                                                             2600                                                                             -10                                            45   40 44  16 1.0                                                                              0.5                                                                              0.5 37.8                                                                             8500                                                                              +1                                            46   43 38  19 1.0                                                                              0.5                                                                              0.5 38.1                                                                             6800                                                                             +48                                            47   43 48   9 0.5                                                                              3.0                                                                              1.0 39.7                                                                             6500                                                                             +27                                             48* 43 48   9 0.5                                                                              20.0                                                                             8.0 not sintered                                         49   43 48   9 2.0                                                                              10.0                                                                             1.0 37.6                                                                             5100                                                                             +22                                             50* 43 48   9 10.0                                                                             10.0                                                                             8.0 32.2                                                                             2000                                                                             +24                                            __________________________________________________________________________

From the results shown in Table 2, the dielectric composition of thepresent invention have a high Q value even at 7 GHz, a relatively highdielectric constant and stable sintering properties. For example, thespecimen No. 41 has a Q value of 9000 at 7 GHz, a dielectric constant of38.0, and a temperature coefficient of resonant frequency [TC(fo)] of 0ppm/°C.

For the specimen No. 41, measurement was made on the quality factor (Q)at various frequencies within the range from 0.5 GHz to 7 GHz. Resultsare shown in FIG. 2 as a function of frequency together with those forthe comparative specimen prepared in Example 1.

From the results shown in FIG. 2, it will be seen that the dielectricceramic composition according to the present invention is improved inthe quality factor (Q). In particular, the quality factor (Q) is muchimproved in lower frequency region. For example, the Q values of thedielectric ceramic bodies at various frequencies are 40,000 at 1 GHz,17,000 at 4 GHz, and 9000 at 7 GHz, which are respectively increased by60 %, 42%, and 29 wt % of those of the comparative specimen.

For the specimen No. 41, measurements were made on crystal grain sizesand mechanical strength. It was found that this composition has a grainsize distribution ranging from 5 to 10 μm and a mechanical strength of1200 Kg/cm². Thus, it will be seen that the incorporation of Ta₂ O₅together with ZnO and NiO makes it possible to obtain dielectricceramics with a fine crystal grain size and a large strength and thatthe addition of these additives contribute to make the grain growthuniform and to inhibit formation of lattice irregularities in the graincrystals.

EXAMPLE 3

Using highly purified oxides TiO₂, ZrO₂, SnO₂, ZnO, NiO and WO₃ as rawmaterials, mixtures of raw materials were so prepared that each of theirsintered bodies has a composition shown in Table 3. Each resultingmixture was wet milled in a mill for 16 hours, dehydrated, dried andthen pressed into discs having a diameter of 12 mm and a thickness of 6mm under a pressure of 2500 kg/cm². The discs were fired in naturalatmosphere at 1350° to 1450° C. for 4 hours to prepare ceramic discs.

Each resultant ceramic disc was subjected to measurements of electricalproperties. The measurements were made on the dielectric constant (ε),quality factor (Q) and temperature coefficient of resonant frequency[TC(fo)] in the same manner under the same conditions as in Example 1.Results are also shown in Table 3.

In the table, asterisked specimens are those having a composition beyondthe scope of the present invention, while other specimens are thoseincluded in the scope of the present invention.

For the specimens Nos. 57, 64, and 73, the measurements of electricalproperties were not carried out since it is impossible to sinter them.

                                      TABLE 3                                     __________________________________________________________________________    Specimen                                                                      No.  TiO.sub.2                                                                        ZrO.sub.2                                                                         SnO.sub.2                                                                        ZnO                                                                              NiO                                                                              WO.sub.3                                                                         ε                                                                        Q  TC(× 10.sup.-6 /°C.)               __________________________________________________________________________     51* 20 56  24 1.0                                                                              0.2                                                                              0.5                                                                              32.2                                                                             6800                                                                             -12                                             52   22 52  26 2.0                                                                              5.0                                                                              5.0                                                                              31.5                                                                             7100                                                                              -9                                             53   22 58  20 3.0                                                                              6.0                                                                              7.0                                                                              28.1                                                                             5200                                                                             +30                                              54* 22 58  20 8.0                                                                              5.0                                                                              10.0                                                                             23.8                                                                             2000                                                                             +42                                             55   28 48  24 1.0                                                                              0.5                                                                              0.5                                                                              31.4                                                                             7800                                                                             -11                                             56   28 56  16 5.0                                                                              3.0                                                                              2.0                                                                              30.8                                                                             6000                                                                             +18                                              57* 32 52  16 0.5                                                                              20.0                                                                             1.0                                                                              not sintered                                          58   32 52  16 2.0                                                                              3.0                                                                              3.0                                                                              31.2                                                                             7400                                                                              -6                                             59   32 52  16 2.0                                                                              10.0                                                                             5.0                                                                              30.1                                                                             5400                                                                              +3                                              60* 32 52  16 10.0                                                                             3.0                                                                              10.0                                                                             24.9                                                                             2100                                                                              -3                                             61   33 58   9 2.0                                                                              4.0                                                                              4.0                                                                              35.7                                                                             5500                                                                             + 29                                            62   36 38  26 3.0                                                                              1.0                                                                              1.0                                                                              36.2                                                                             7700                                                                              +9                                             63   38 48  14 1.0                                                                              0.5                                                                              1.0                                                                              38.0                                                                             8000                                                                              +1                                              64* 38 48  14 10.0                                                                             20.0                                                                             6.0                                                                              not sintered                                           65* 40 36  24 1.0                                                                              0.5                                                                              0.5                                                                              40.1                                                                             4700                                                                             +78                                             66   40 39  21 0.5                                                                              0.2                                                                              1.0                                                                              37.9                                                                             8700                                                                               0                                             67   40 39  21 1.0                                                                              0.5                                                                              2.0                                                                              36.3                                                                             8500                                                                              -4                                              68* 40 39  21 2.0                                                                              20.0                                                                             7.0                                                                              23.9                                                                             2300                                                                              +9                                              69* 40 39  21 7.0                                                                              5.0                                                                              10.0                                                                             24.6                                                                             2500                                                                              -7                                             70   40 44  16 1.0                                                                              0.5                                                                              0.5                                                                              37.5                                                                             8300                                                                              +2                                             71   43 38  19 1.0                                                                              0.5                                                                              0.5                                                                              37.9                                                                             7100                                                                             +45                                             72   43 48   9 0.5                                                                              3.0                                                                              1.0                                                                              39.9                                                                             6500                                                                             +24                                              73* 43 48   9 0.5                                                                              20.0  not sintered                                          74   43 48   9 2.0                                                                              10.0                                                                             1.0                                                                              37.0                                                                             4600                                                                             +20                                              75* 43 48   9 10.0                                                                             10.0                                                                             8.0                                                                              31.5                                                                             2000                                                                             +29                                             __________________________________________________________________________

From the results shown in Table 3, the dielectric compositions of thepresent invention have a high Q value even at 7 GHz, a relatively highdielectric constant and stable sintering properties. For example, thespecimen No. 66 has a Q value of 8700 at 7 GHz, a dielectric constant of37.9, and a temperature coefficient of resonant frequency [TC(fo)] of 0ppm/°C.

For the specimen No. 66, measurement was made on the quality factor (Q)at various frequencies within the range from 0.5 GHz to 7 GHz. Resultsare shown in FIG. 3 as a function of frequency together with those forthe comparative specimen prepared in Example 1.

From the results shown in FIG. 3, it will be seen that the dielectricceramic composition according to the present invention is improved inthe quality factor (Q). In particular, the quality factor (Q) increasesquite rapidly with lowering of frequency. For example, its Q values are38,000 at 1 GHz, 16,000 at 4 GHz, and 8700 at 7 GHz, which arerespectively increased by 52%, 33%, and 24% of those of the comparativespecimen.

For the specimen No. 66, measurements were also made on crystal grainsizes and mechanical strength. It was found that this composition has agrain size distribution ranging from 5 to 10 μm and a mechanicalstrength of 1200 Kg/cm². Thus, it will be seen that the incorporation ofWO₃ together with ZnO and NiO makes it possible to obtain dielectricceramics with a fine crystal grain size and a large strength and thatthe addition of these additives contribute to make the grain growthuniform and to inhibit formation of lattice irregularities in the graincrystals.

EXAMPLE 4

Using highly purified oxides TiO₂, ZrO₂, SnO₂, ZnO, NiO and Sb₂ O₅ asraw materials, mixtures of these raw materials were so prepared thateach of their sintered bodies has a composition shown in Table 4. Eachresulting mixture was wet milled in a mill for 16 hours, dehydrated,dried and then pressed into discs having a diameter of 12 mm and athickness of 6 mm under a pressure of 2500 kg/cm². The discs were firedin natural atmosphere at 1350° to 1450° C. for 4 hours to prepareceramic discs.

Each resultant ceramic disc was subjected to measurements of electricalproperties. The measurements were made on the dielectric constant (ε),quality factor (Q) and temperature coefficient of resonant frequency[TC(fo)] in the same manner under the same conditions as in Example 1.Results are also shown in Table 4.

In the table, asterisked specimens are those having a composition beyondthe scope of the present invention, while other specimens are thoseincluded in the scope of the present invention. For the specimens Nos.82, 89, and 98, the measurements of electrical properties were notcarried out since it is impossible to sinter them.

                                      TABLE 4                                     __________________________________________________________________________    Specimen                                                                      No.  TiO.sub.2                                                                        ZrO.sub.2                                                                         SnO.sub.2                                                                        ZnO                                                                              NiO                                                                              Sb.sub.2 O.sub.5                                                                  ε                                                                        Q  TC(× 10.sup.-6 /°C.)              __________________________________________________________________________     76* 20 56  24 1.0                                                                              0.2                                                                              0.5 31.8                                                                             7000                                                                             -12                                            77   22 52  26 2.0                                                                              5.0                                                                              5.0 30.6                                                                             7200                                                                             -10                                            78   22 58  20 3.0                                                                              6.0                                                                              7.0 27.9                                                                             5300                                                                             +30                                             79* 22 58  20 8.0                                                                              5.0                                                                              10.0                                                                              25.4                                                                             2600                                                                             +39                                            80   28 48  24 1.0                                                                              0.5                                                                              0.5 30.8                                                                             7700                                                                             -11                                            81   28 56  16 5.0                                                                              3.0                                                                              2.0 30.0                                                                             5600                                                                             +19                                             82* 32 52  16 0.5                                                                              20.0                                                                             1.0 not sintered                                         83   32 52  16 2.0                                                                              3.0                                                                              3.0 31.0                                                                             7700                                                                              -2                                            84   32 52  16 2.0                                                                              10.0                                                                             5.0 29.8                                                                             5600                                                                               0                                             85* 32 52  16 10.0                                                                             3.0                                                                              10.0                                                                              24.8                                                                             2300                                                                              -3                                            86   33 58   9 2.0                                                                              4.0                                                                              4.0 36.0                                                                             5500                                                                             +27                                            87   36 38  26 3.0                                                                              1.0                                                                              1.0 36.2                                                                             7800                                                                              +9                                            88   38 48  14 1.0                                                                              0.5                                                                              1.0 38.2                                                                             8000                                                                              +3                                             89* 38 48  14 10.0                                                                             20.0                                                                             6.0 not sintered                                          90* 40 36  24 1.0                                                                              0.5                                                                              0.5 40.2                                                                             5300                                                                             +75                                            91   40 39  21 0.5                                                                              0.2                                                                              1.0 37.8                                                                             8700                                                                               0                                            92   40 39  21 1.0                                                                              0.5                                                                              2.0 36.2                                                                             8500                                                                              -4                                             93* 40 39  21 2.0                                                                              20.0                                                                             7.0 23.0                                                                             1600                                                                              +3                                             94* 40 39  21 7.0                                                                              5.0                                                                              10.0                                                                              24.1                                                                             2000                                                                             -12                                            95   40 44  16 1.0                                                                              0.5                                                                              0.5 37.5                                                                             7900                                                                              -1                                            96   43 38  19 1.0                                                                              0.5                                                                              0.5 37.8                                                                             6500                                                                             +49                                            97   43 48   9 0.5                                                                              3.0                                                                              1.0 39.3                                                                             6000                                                                             +27                                             98* 43 48   9 0.5                                                                              20.0                                                                             8.0 not sintered                                         99   43 48   9 2.0                                                                              10.0                                                                             1.0 37.4                                                                             4800                                                                             +23                                            100* 43 48   9 10.0                                                                             10.0                                                                             8.0 32.0                                                                             2200                                                                             +25                                            __________________________________________________________________________

From the results shown in Table 4, the dielectric compositions of thepresent invention have a high Q value even at 7 GHz, a relatively highdielectric constant and stable sintering properties. For example, thespecimen No. 91 has a Q value of 8700 at 7 GHz, a dielectric constant of37.8 and a temperature coefficient of resonant frequency [TC(fo)] of 0ppm/°C.

For the specimen No. 91, measurement was made on the quality factor (Q)at various frequencies within the range from 0.5 GHz to 7 GHz. Resultsare shown in FIG. 4 as a function of frequency together with those forthe comparative specimen prepared in Example 1.

From the results shown in FIG. 4, it will be seen that the dielectricceramic composition according to the present invention is improved inthe quality factor (Q). In particular, the quality factor (Q) is muchimproved in lower frequency region. For example, its Q values are 38,000at 1 GHz, 16,000 at 4 GHz, and 8700 at 7 GHz, which are respectivelyincreased by 52%, 33%, and 24 wt % of those of the comparative specimen.

For the specimen No. 91, measurements were made on crystal grain sizesand mechanical strength. It was found that this composition has a grainsize distribution ranging from 5 to 10 μm and a mechanical strength of1200 Kg/cm². Thus, it will be seen that the incorporation of Sb₂ O₅together with ZnO and NiO makes it possible to obtain dielectricceramics with a fine crystal grain size and a large strength. It isbelieved that the addition of these additives contribute to make thegrain growth uniform and to inhibit formation of lattice irregularitiesin the grain crystals.

What we claim is:
 1. A dielectric ceramic composition for highfrequencies consisting essentially of a main component of a TiO₂ -ZrO₂-SnO₂ system and additives composed of ZnO, NiO, and one metal oxideselected from the group consisting of Nb₂ O₅, Ta₂ O₅, WO₃ and Sb₂ O₅,said main component consisting essentially of 22 to 43 wt % of TiO₂, 38to 58 wt % of ZrO₂, and 9 to 26 wt % of SnO₂, the content of ZnO beingnot more than 7 wt %, the content of NiO being not more than 10 wt %,the content of one metal oxide selected from the group consisting of Nb₂O₅, Ta₂ O₅, WO₃ and Sb₂ O₅ being not more than 7 wt %.
 2. The dielectricceramic composition according to claim 1 containing 40 weight % TiO₂, 39weight % ZrO₂, 21 weight % of SnO₂, as said main component and, asadditives, 0.5% of ZnO, 0.2% of NiO and 1 weight % of said metal oxide.3. The dielectric ceramic composition according to claim 1 containing,as additives, not more than 7 wt % of ZnO, not more than 10 wt % of NiO,and not more than 5 wt % of Nb₂ O₅.
 4. The dielectric ceramiccomposition according to claim 3 containing, as additives, 0.5 to 5weight % ZnO, 0.2 to 10 weight % of NiO and 0.5 to 5 weight % of Nb₂ O₃.5. The dielectric ceramic composition according to claim 1 containing,as additives, not more than 7 wt % of ZnO, not more than 10 wt % of NiO,and not more than 7 wt % of Ta₂ O₅.
 6. The dielectric ceramiccomposition according to claim 5 containing, as additives, 0.05 to 5weight % ZnO, 0.2 to 10 weight % of NiO and 0.5 to 7 weight % of Ta₂ O₅.7. The dielectric ceramic composition according to claim 1 containing,as additives, not more than 7 wt % of ZnO, not more than 10 wt % of NiO,and not more than 7 wt % of Sb₂ O₅.
 8. The dielectric ceramiccomposition according to claim 7 containing, as additives, 0.5 to 5weight % ZnO, 0.2 to 10 weight % of NiO and 0.5 to 7 weight % of Sb₂ O₅.9. The dielectric ceramic composition according to claim 1 containing,as additives, not more than 7 wt % of ZnO, not more than 10 wt % of NiO,and not more than 7 wt % of WO₃.
 10. The dielectric ceramic compositionaccording to claim 9 containing, as additives, 0.5 to 5 weight % ZnO,0.2 to 10 weight % of NiO and 0.5 to 7 weight % of WO₂.